This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Seneca Valley Virus (SVV-001) is an oncolytic RNA virus classified within the family Picornaviridae that has been shown to be selective and potent toward killing tumor cells having one or more neuroendocrine properties in both in vitro and in vivo studies. This phase I study will evaluate the toxicities, viral clearance (pharmacokinetics), and clinical activity of SVV-001 in children with relapsed/refractory neuroblastoma, rhabdomyosarcoma, Ewing Family of tumors, or rare tumors with neuroendocrine features (Wilms- tumor, retinoblastoma, adrenocortical carcinoma or carcinoid tumors). Cohorts of three to six patients will receive a single 1 hour infusion of SVV-001 at a starting dose of 1x109 viral particles (vp) per kilogram (vp/kg) (2-logs below the adult starting dose). The starting dose will be escalated by 1-log increments in additional cohorts of three to six patients until the maximum tolerable dose is determined or 1x1012 vp/kg is reached in dose level 4.